Free The First War of Physics by Jim Baggott Page B

subject to strict secrecy. Briggs remained as chairman of the committee, reporting to James Bryant Conant, president of Harvard, who had joined the NDRC at Bush’s invitation. The dependence on sceptical military advisers for funding was now greatly reduced.
    Not that this made a great deal of difference, however. Bush and Conant were very aware of the potential threat of a German atomic bomb, but instead of lobbying to secure greatly increased funding for the American nuclear programme they preferred rather to focus research efforts on proving that a bomb was impossible. After all, if it could not be done then there would never be a threat from a German weapon. In a report to the NDRC dated 1 July 1940, Briggs summarised the progress to date and requested $40,000 for further critical research on the nuclear properties of the materials involved and $100,000 for experiments on a large-scale uranium–graphite pile. Briggs got the $40,000.
    Szilard was left to wait a while longer.
    The creation of the NDRC produced one unlooked-for side-effect. This was an American organisation involved in secret military research projects – only US citizens could be members. Fermi, Szilard, Teller and Wigner were now suddenly excluded from the proceedings. This was obviously absurd, and Sachs argued strenuously that the entire work of the Advisory Committee had depended on the efforts of emigre scientists who were now to be barred from future involvement.
    Military security checks were duly carried out. The security report on Fermi labelled him ‘undoubtedly a Fascist’ (he was not) and recommended that he should not be employed on secret work. The report on Szilard suggested that he was ‘very pro-German’ and had ‘remarked on many occasions that he thinks the Germans will win the war’. The report recommended that Szilard, too, be barred from employment on secret work. Both reports quoted ‘highly reliable sources’. The irony was lost on them. The only secrets worth protecting were in the minds of the very scientists the authorities wanted to exclude.
    The reports were sent to J. Edgar Hoover in August 1940 with a request for further FBI security checks. The FBI merely repeated what the military authorities had already claimed. It appeared not to matter. Sachs’ arguments won the day. All four émigré’ physicists were allowed to continue to make their contributions to the project, but now as advisers to the NDRC rather than full members.
    Despite its now greatly raised profile, the work still proceeded slowly. In fairness, the results obtained thus far painted a rather confused picture. U-235 was clearly responsible for slow-neutron fission in uranium but separation of this isotope from U-238 was going to be an incredibly difficult feat. The early signs pointing to the feasibility of a uranium reactor were both encouraging and discouraging. Graphite in a suitably pure form would serve as a suitable moderator, but it was still not yet known if a self-sustaining chain reaction would develop in a uranium reactor without considerable enrichment of the minor U-235 isotope. Nier and Dunning’s conclusions in this regard had not been very promising. If a working reactor could be built, resonant absorption of neutrons by U-238 in such areactor might produce element 94, which could be more easily separated from uranium and which might prove to be fissionable in its own right.
    To cap it all, Teller had carried out some calculations which suggested that a uranium bomb would require a mass of more than 30 tons. Even if it could be made to explode, it was difficult to see how such a bomb could be delivered to its target.
    Bush remained sceptical of the science. It was difficult to see all this as anything other than a wild goose chase.
    Thousands of times more powerful
    The reckless, naked aggression that had been unleashed in Europe by Nazi Germany shaped the attitudes of all who observed it from across the Atlantic, but its effect on